An Integrated Frequency Control for Grid-connected Wind Farm Based on VSC-HVDC

As to the frequency decoupling characteristics of AC system at the two sides of wind farm by using grid-connected mode of voltage source converter based high voltage direct current(VSC-HVDC ), the frequency can not be regulated by traditional control method. By combing virtual inertial control, droop control and quick charging and discharging theory of DC capacity, an integrated frequency control is proposed for varying DC voltage control unit added on inverter at grid side of VSC-HVDC, in which regulated DC bus voltage is taken as frequency control signal of wind turbines. When grid frequency fluctuates because of the power imbalance, then DC voltage level of VSC-HVDC varies by using the proposed control method,and energy stored in the DC capacitor will be released or absorb. Furthermore, the voltage value is transmitted to wind farm as frequency regulating signal, which make wind turbine absorb or release kinetic energy, and provides dynamic support for grid frequency. Simulation results verify the validity of proposed integrated frequency control method.